System and method for reducing gaseous microemboli using venous blood bypass with filter

ABSTRACT

A system and method for reducing gas bubbles, including gaseous microemboli (GME) during cardiopulmonary bypass (CPB) by the use of an oxygenator with venous blood bypass and a filter in the venous blood bypass is provided.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation application of application Ser. No.16/322,513, filed Feb. 1, 2019, which claims priority to and the benefitof U.S. provisional patent application Ser. No. 62/369,262, filed onAug. 1, 2016, the contents of which is included herein by reference intheir entireties.

FIELD

The disclosure relates to a system and method for cardiopulmonarybypass, and more particularly to a system and method to reduce gaseousmicroemboli (GME) using an oxygenator with venous bypass and a filter.

BACKGROUND

There is a need to replace the function of the heart and lungs byartificial means, such as during heart operations. Also in more chronicdisease states, for example during severe pulmonary, cardiac, or renalfailure, maintenance of life can be upheld by different artificial meansuntil an organ for transplantation becomes available. In many clinicalsituations there is a need for an extracorporeal circuit wherein anartificial organ is incorporated.

Gas bubbles are easily formed in blood and are propelled into thecirculation of a living being during extracorporeal circulation. Gasbubbles are formed from many sources, including cavitation, temperaturegradients, and differences in the amount of gases dissolved between asubject's own and incoming blood, as well as inadvertent physicalintroduction of gas bubbles into blood by caregivers during surgicalmanipulation or parenteral administration of fluids. In the case ofheart surgery, the extracorporeal circuit contains a gas-exchangedevice, for example an oxygenator, which is used for oxygenation andremoval of carbon dioxide, for example. The close contact between bloodand gas in the oxygenator poses significant risks for inadvertent entryof gas bubbles into the circulating blood.

At present, to avoid bubble formation during heart surgery,membrane-type oxygenators are used instead of bubble-oxygenators, hightemperature gradients are avoided, and use of suction in the operatingfield is controlled. Heart-lung machines contain an air bubble sensorthat warns the person controlling the heart-lung machine of theappearance of small bubbles, and immediately stops the main pump whenlarger bubbles appear. Typically, the bubble sensor can discern bubbleswith a diameter of approximately 0.3 millimeters (mm) or larger, andstops the main pump when a bubble with a diameter of 3-5 mm isrecognized.

Cardiac surgery is frequently complicated by postoperativeneurocognitive deficits that degrade functional capacity and quality oflife while increasing healthcare costs. Multifactorial contributors tothis significant public health problem likely include gaseousmicroemboli (GME). The arterial circulation receives thousands of 10-40micrometer (μm) diameter GME during cardiopulmonary bypass (CPB),despite the use of membrane oxygenation and arterial filtration.Vasooclusive GME cause tissue ischemia and denude endothelium in thebrain and other end organs, leading to vascular dilation, increasedpermeability, activation of platelets and clotting cascades, andrecruitment of complement and cellular mediators of inflammation.

Current perfusion practice targets mildly hyperoxic blood gases duringCPB, by lowering the partial pressure of oxygen in oxygenator sweep gasby dilution with air, thereby producing the needless side effect ofdissolving nitrogen in blood. The blood, thus saturated with dissolvedgas, is poorly able to dissolve gases that exist in bubble form as GME.

Nonetheless, there remains a need to prevent or reduce the generation ofgas bubbles, e.g., the formation of gas bubbles during heart surgery. Ina blood bubble, in the liquid-gas interface, there is an approximately40-100 Angstroms (Å) (4-10 nanometer) deep layer of lipoproteins thatdenaturate due to direct contact with the foreign material, e.g., gas.In turn, the Hageman factor is activated, which initiates coagulationand the concomitant adverse consumption of factors promotingcoagulation, which are used to prevent bleeding from the surgical wound.

Accordingly, a system and method capable of inhibiting the bubbleformation in the blood, as well as reducing the number and size ofbubbles during extracorporeal circulation, is needed.

SUMMARY

Disclosed herein is a system and method for reducing gas bubbles,including gaseous microemboli (GME) during cardiopulmonary bypass (CPB).This approach reduces the number and size of GME, which can be useful inreducing postoperative complications, including neurocognitive deficitsin CPB and other procedures. The system and method can be used for bothin vitro and in vivo approaches. The system and method can be used inhypobaric and normobaric conditions.

A system for reducing gaseous microemboli, the system comprising a fluidsource; a flow diverter fluidly connected to the fluid source, whereinthe flow diverter is configured to remove a portion of the fluid fromthe fluid source; an inflow flow controller fluidly connected to thefluid source, wherein the inflow flow controller is configured tocontrol the flow rate of fluid from the fluid source to the flowdiverter; a bypass line fluidly connected to the flow diverter; a bypassflow controller fluidly connected to the bypass line, wherein the bypassflow controller is configured to control the flow rate of fluid from thebypass line; a filter in fluid communication with the bypass line,wherein the filter removes gaseous microemboli having a diameter greaterthan a stated pore size, preferably 15 to 50 micrometers; an oxygenatorfluidly connected to the fluid source, wherein the oxygenator isconfigured to oxygenate the fluid from the fluid source; an outflow flowcontroller fluidly connected to the oxygenator, wherein the outflow flowcontroller is configured to control the flow rate of fluid from theoxygenator; an outlet fluidly connected to the oxygenator and the bypassline; a controller configured to control the inflow flow controller, thebypass flow controller, the outflow flow controller, or a combinationcomprising at least one or more of the foregoing, is provided.

A method for reducing gaseous microemboli, the method comprisingproviding an oxygenator configured to oxygenate a fluid, the oxygenatorhaving a venous inlet, an arterial outlet, a venous bypass line fluidlyconnected to the venous inlet and the arterial outlet, wherein thevenous bypass line comprises a filter configured to remove gaseousmicroemboli having a diameter greater than a stated pore size,preferably 15 to 50 micrometers, and wherein the venous bypass line isconfigured to remove a portion of the fluid from the venous inlet;introducing a fluid to the oxygenator; oxygenating the fluid passingthrough the oxygenator; combining the fluid from the venous bypass lineand the arterial outlet, forming a combined fluid; wherein the partialpressure of dissolved oxygen in the combined fluid is 100 to 700millimeters of mercury (mmHg), preferably 150 to 250 mmHg, is provided.

BRIEF DESCRIPTION OF THE FIGURES

The accompanying drawings incorporated in and forming a part of thespecification embody several aspects of the present disclosure and,together with the description, serve to explain the principles of thisdisclosure. In the drawings:

FIG. 1 is a schematic representation of an embodiment of a CPB systemusing a venous bypass with filter.

FIG. 2 is a schematic representation of an oxygenator that can be used.

FIG. 3 shows a heart-lung machine circuit used to obtain the dataprovided here.

FIG. 4 shows experimental data showing the fraction of total flowtraveling through the shunt limb over a large range of total flow rates.

FIG. 5 shows experimental data showing the partial pressure of dissolvedCO₂ or O₂ under three different conditions.

FIG. 6 shows experimental data showing reduction of GME at two locationsin a CPB system.

FIG. 7 shows experimental data showing reduction of GME delivery throughthe shunt limb in the presence of an arterial filter at three locationsin the CPB bypass circuit.

FIG. 8 shows the sum of the partial pressures as a function of the shuntfraction.

DETAILED DESCRIPTION

The following disclosure will detail particular exemplary embodiments,which provide methods and systems for reducing GME in a CPB system. Anoverview of the mechanism and methods used herein is provided.

The inventor hereof has unexpectedly solved the practical problem ofshunting of GME around an oxygenator, by using an arterial filter in theshunt limb, in an embodiment.

This disclosure is directed to reduction of GME during CPB and otherprocedures including extracorporeal membrane oxygenation (ECMO),including veno-arterial ECMO and veno-venous ECMO, by the use of anoxygenator with venous blood bypass and a filter in the venous bloodbypass. The systems and methods described can also be used forextracorporeal circulation systems including dialysis, continuousveno-venous hemofiltration (CVVH), and heart ventricular assist devices(VAD). Venous blood bypass takes a portion of the blood from the venoussystem or other source of non-oxygenated blood, bypasses the oxygenator,and introduces the bypassed venous blood into blood coming from theoxygenator. This mixture of oxygenated and non-oxygenated blood reducesthe concentration of oxygen in the blood coming from the oxygenator,promoting removal of microbubbles from the blood. This approach allowsthe operation of the oxygenator using pure oxygen, nitrogen-free sweepgas, thereby avoiding both hyperoxemia that may be damaging to thepatient and dissolved nitrogen that may oppose dissolution and removalof microbubbles

Although Applicant is not bound by any theory presented here, it isbelieved the mechanism for reducing GME described here involves reducingthe sum of partial pressures of dissolved gases in the arterial bloodreturning to the patient, thereby permitting reabsorption of gases frombubbles into the blood phase.

In an embodiment, the gas profile in the mixed arterial blood travelingto the patient is around 150-250 mmHg dissolved oxygen (around 100 mmHgis the normal value in a healthy human) plus around 40 mmHg dissolvedCO₂, for a sum of partial pressures of dissolved gases of 190-290 mmHg,which is hypobaric compared to the approximately 760 mmHg atmosphericpressure.

In an embodiment, all gas emboli, not matter how large or small, areremoved in the filtered circuit. In an embodiment, emboli with diameterlarger than a stated pore size of a filter, for example, between 15 to50 micrometers, for example, greater than 15 micrometers, greater than20 micrometers, greater than 28 micrometers, greater than 32micrometers, greater than 37 micrometers, or greater than 40micrometers, for example, are removed, and particles having a diameterless than the stated pore size pass through. In an embodiment, embolihaving diameter larger than 50 micrometers, preferably larger than 40micrometers, preferably larger than 28 micrometers are removed from thefiltered circuit. Emboli in this size range are considered large enoughto occlude capillaries but small enough to pass through an arterialfilter.

As used herein, “fluid” and “blood” are used interchangeably, except asotherwise noted. It is to be understood that the systems and methods canbe used for blood, or other fluids, such as a blood substitute,artificial blood, a blood product, such as plasma or albumin, plateletsor plasma concentrates, crystalloids such as saline, lactated ringer'ssolution, normosol, plasmalyte, hetastarch, or other fluid, or acombination comprising at least one of the foregoing.

The fluid source can be from a subject, such as an animal, for example ahuman, or other mammal. The fluid source can be from a subject usingcannulae inserted into the subject's venous or arterial system or heartchambers or body cavities, a fluid reservoir, or from a source outside asubject. The subject can be a patient undergoing treatment orevaluation.

The filter, because it acts as a resistance to flow, can be used toadjust or control flow in the bypass line.

A flow diverter is used to divert a portion of the blood and can be anysuitable apparatus used to remove a portion of the fluid from the fluidsource, such as a tubing tee, or a pump, or a separate non-gas-exchangeshunt channel through an oxygenator.

The use of a separate non-gas-exchange shunt channel through anoxygenator can use 1) a filtered or non-filtered shunt channel withinthe oxygenator itself, the flow through which may or may not beregulatable or user-determined; or 2) a means of flowing sweep gasselectively to only a fraction of the sweep gas microtubules in theoxygenator fiber bundle, thereby allowing non-gas-exchange shunting tooccur within the oxygenator without defeating the oxygenator'sfiltration role, for example. 2a) This approach can use a variable flapor device comprised of rubber, gel, polymer, foam, wax, plastic, metal,or other suitable material or reversible occlusion device to prevent gasflow through a portion of the fiber bundle near the sweep gas inlet orwithin the sweep gas inlet manifold, near the sweep gas outlet or withinthe sweep gas outlet manifold, or both, or anywhere along the sweep gasflow path. There can be more than one occlusion device used in a device,and a user or controller may be able to engage them in a desiredcombination to produce the desired amount of non-gas-exchange shunting.The occlusion may also be performed using a fluid or other suitablesubstance instilled into the sweep gas inlet manifold, or sweep gasoutlet manifold, or both, for example water, oil, polymer, foam, or wax,2b) This approach may also use a fluid or other suitable substance suchas water, saline, crystalloid, colloid, blood product, oil, gel,polymer, foam, or wax instilled permanently or reversibly into the sweepgas inlet manifold or the sealed or unsealed sweep gas outlet manifold,or both, in order to prevent flow through a fraction of the sweep gasmicrotubules of the fiber bundle. Extra ports in dependent ornon-dependent portions of the sweep gas inlet manifold or the sweep gasoutlet manifold, or both, may be required to allow instillation andremoval of substances to regulate sweep gas flow in the fiber bundle.Positive pressure relief valves in the sweep gas inlet manifold or thesweep gas outlet manifold, or both, may be required to relieve positivepressures that may result from limitation of sweep gas flow to afraction of the fiber bundle. 2c) A non-gas-exchange shunt channelthrough an oxygenator can also be performed by dividing the oxygenatorinto compartments or using multiple oxygenators, where each compartmentor oxygenator receives blood flow but the user can decide whether andhow much sweep gas to flow in some of the compartments or oxygenators toachieve the desired level of non-gas-exchange shunting.

3) In the case of an oxygenator employing multiple compartments orduring the use of multiple oxygenators, the same desirable effects ondissolved gases in blood and GME removal may be achieved in the absenceof non-gas exchange shunting by directing blood and sweep gas flow to aminimum number of compartments or oxygenators necessary to achieve auser-defined oxygenation target but no more. The amount and flowcharacteristics of the fluid coming from the fluid source, such as flowvelocity, flow volume, or other characteristic into the flow divertercan be controlled by an inflow controller, such as a needle valve, amass flow controller, pump, or partial occlusion clamp. The inflowcontroller can be controlled independently, or can be controlled by acontroller configured to control other aspects of the system, asdescribed further herein.

The bypass line can be any suitable material, such as medical gradetubing, or other materials known to one of ordinary skill in the artwithout undue experimentation. The diameter, length, and composition ofthe bypass line is easily determined by one of ordinary skill in the artwithout undue experimentation.

The flow of fluid in the bypass line can be further controlled, forexample to achieve the desired characteristics of fluid in the outlet. Asensor can be used in any desirable or useful location in the system todetermine the actual or approximate number and size of GME or otherparticles, concentration of anticoagulants, anesthesia, or othermedication, concentration of gases, such as oxygen, nitrogen, carbondioxide, oxygen saturation of blood hemoglobin, or flow rate, forexample. Flow rate and oxygen saturation sensors are applied external tothe tubing and are standard. Blood samples are removed frequently, andin some cases continuously, for more detailed blood gas andanticoagulant analysis. The composition or other characteristics of thefluid in the bypass line can be altered from the composition or othercharacteristics of the fluid in the fluid source. For example,medication, such as anticoagulants or other medication, or gases, suchas oxygen, nitrogen, carbon dioxide, or air, for example, can be addedor removed to achieve the desired level of gases and other components.

In embodiments, a sensor is introduced at a location in the bypass linebefore the filter, a location in the bypass line after the filter, or acombination comprising one or more of the foregoing, to achieve thedesired level of oxygen and other substances in the fluid in the bypassline.

A filter is inserted in the bypass line. The filter can be a so-called“arterial filter”, as known in the art, designed to remove bubbles(GME), lipids, and other debris having a diameter greater than a statedpore size, for example, greater than 15 micrometers, greater than 20micrometers, greater than 28 micrometers, greater than 32 micrometers,greater than 37 micrometers, or greater than 40 micrometers, forexample, and let particles having a diameter less than the stated poresize pass through.

The filter pore size should be small enough to remove bubbles, but notso small as to prevent desired blood flows at reasonable pressures,known to one of ordinary skill in the art, or cause damage or filteringof cellular elements. The filter can also be a hemoconcentrator, bubbletrap, or oxygenator, any of which may be operated under vacuum. Thefilter can be made from any suitable material, such as polyester.

The oxygenator can be any of a number of devices, such as a membraneoxygenator, a diffusion membrane oxygenator, or a hollow fibermicroporous membrane oxygenator. In an embodiment, the oxygenator is amicroporous membrane oxygenator with or preferably without a sealedhousing. In an embodiment, the oxygenator is a microporous membraneoxygenator without a sealed housing. The connections of the fluid to andfrom the oxygenator, to and from the bypass line, and other connectionsare those known by one of ordinary skill in the art without undueexperimentation. The operation of the oxygenator is known by one ofordinary skill in the art without undue experimentation.

The flow rate and volume, as well as other desired characteristics, of afluid at any point in the system can be controlled by a flow controller,or other suitable device. A flow controller can be a needle valve, amass flow controller, a pump, a clamp, or a partial occlusion clamp.

An outlet is fluidly connected to the oxygenator and the bypass line.The outlet can be the point where the fluid from the bypass line and theoxygenator are combined. A sensor can be used to measure a desiredcharacteristic of the fluid at the outlet, for example, theconcentration of anticoagulants or other medication, concentration ofgases, such as oxygen, nitrogen, carbon dioxide, air, or blood oxygensaturation.

After the fluid is passed through the oxygenator and combined with thefluid from the venous bypass, the fluid can be stored, or reinfused intoa subject or patient, for example.

Parameters of the system can be controlled by a controller, configuredto control the inflow flow controller, the bypass flow controller, theoutflow flow controller, or a combination comprising at least one ormore of the foregoing. Each of the parameters of the system can also becontrolled independently, such as by use of a manual valve.

In an embodiment, 0 to 50 percent of the total volume of the bloodcoming from the patient into the CPB system is diverted to the venousbypass. In an embodiment, 0 to 40 percent of the total volume of theblood coming from the patient into the CPB system is diverted to thevenous bypass. In an embodiment, 0 to 30 percent of the total volume ofthe blood coming from the patient into the CPB system is diverted to thevenous bypass. In an embodiment, 0 to 20 percent of the total volume ofthe blood coming from the patient into the CPB system is diverted to thevenous bypass. In an embodiment, 0 to 10 percent of the total volume ofthe blood coming from the patient into the CPB system is diverted to thevenous bypass. In an embodiment, 0 to 5 percent of the total volume ofthe blood coming from the patient into the CPB system is diverted to thevenous bypass. The blood entering the venous bypass can be filtered,cooled, warmed, fortified with various medications or gases, orotherwise treated. In an embodiment, the partial pressure of oxygen atthe outlet is 50 to 800 mmHg. In an embodiment, the partial pressure ofoxygen at the outlet is 100 to 700 mmHg. In an embodiment, the partialpressure of oxygen at the outlet is 75 to 650 mmHg. In an embodiment,the partial pressure of nitrogen at the outlet is zero. In anembodiment, the partial pressure of nitrogen at the outlet is minimized.In an embodiment, the partial pressure of nitrogen at the outlet is anonzero level up to about 600 mmHg.

The desired parameters/composition of blood or fluid at the outlet (thepoint of mixing between blood from the oxygenator and blood from theshunt) depends on the goals of the surgical team and perfusionist forthe patient. Frequently, the perfusionist will target an oxygen tensionof 150-250 mmHg, a CO₂ tension of 40 mmHg, and an overall flow rate thatis reasonably close to the patient's predicted normal cardiac output andwhich generates an adequate blood pressure in the patient's vascularsystem. In a common scenario, the perfusionist may flow 5 L/min of totalflow, comprised of 1.5 L/min of flow through the shunt limb and 3.5L/min of flow through the oxygenator. He or she may raise or lower theshunt fraction to adjust the pO₂, raise or lower the sweep gas flow rateto adjust the pCO₂, or raise or lower the flow rate to adjust the bloodpressure.

In an embodiment, the filter acts to remove gaseous microemboli, as wellas acts as a flow restrictor for the venous blood bypass, which can beused to control the oxygen level of the blood going back to the patient,for example. The method can be used in both normal baric and hypobaricconditions. In an embodiment, the oxygenator is configured to have asubatmospheric pressure, and can have a pressure of 0.4 to 1 atmospheresabsolute. The described shunt can be used together with operating anoxygenator at subatmospheric pressure. In an embodiment, the systemincludes a vacuum regulator fluidly connected to the oxygenator, andconfigured to provide the subatmospheric pressure. In an embodiment, theoxygenator is configured to have atmospheric pressure.

The system can include one or more sensors configured to measure one ormore of flow rate, fluid composition, oxygen saturation, carbon dioxidecontent, nitrogen content, temperature, hematocrit, or a combinationcomprising one or more of the foregoing, wherein the sensor is fluidlyconnected to the fluid source, the bypass line, the outlet, or acombination comprising one or more of the foregoing. These sensors canbe any of a number of common sensors, known to one of ordinary skill inthe art.

In an embodiment, the controller comprises a processor and softwareinstructions implemented by the processor.

The fluid source can be a blender configured to combine one or morefluids.

The system can be used for a number of different fluids, such as blood,a blood substitute, artificial blood, a blood product, such as plasma oralbumin, platelets or plasma concentrates, crystalloids such as saline,lactated ringer's solution, normosol, plasmalyte, hetastarch, or otherfluid, or a combination comprising one or more of the foregoing.

Also provided is a method for reducing gaseous microemboli, the methodincluding providing an oxygenator configured to oxygenate a fluid, theoxygenator having a venous inlet, an arterial outlet; a venous bypassline fluidly connected to the venous inlet and the arterial outlet,wherein the venous bypass line comprises a filter configured to removegaseous microemboli greater than a stated pore size, typically 15 to 50micrometers, or 28 to 40 micrometers, for example, and wherein thevenous bypass line is configured to remove a portion of the fluid fromthe venous inlet; introducing a fluid to the oxygenator; oxygenating thefluid passing through the oxygenator, typically using pure oxygen sweepgas; combining the fluid from the venous bypass line and the arterialoutlet, forming a combined fluid; wherein the concentration of oxygen inthe combined fluid is 75 to 800 mmHg, preferably 100 to 700 mmHg,preferably 100 to 650 mmHg, preferably 150 to 250 mmHg. The oxygenatorcan be any suitable apparatus that can introduce oxygen to a fluid andremove carbon dioxide from a fluid. The method can further includeintroducing medication or gases into the fluid. The method can furtherinclude measuring the concentration of oxygen, nitrogen, carbon dioxide,anesthesia, medication, oxygen saturation, or other substances at anypoint including the blood and the gas at the sweep gas outlet. Themeasuring can be performed using any suitable measurement apparatus orsampling technique, such as the use of an inline dual-wavelengthoximeter, or the use of a sampling technique where a portion of thefluid is removed for analysis. The method can further include monitoringor controlling the temperature of the fluid at any point.

The system and method can also include a non-gas-exchange shunt channelthrough the oxygenator, instead of, or in addition to the shunt limb. Inan embodiment, one of a non-gas-exchange shunt channel through theoxygenator or the shunt limb is used. In an embodiment, anon-gas-exchange shunt channel through the oxygenator is used. Thenon-gas-exchange shunt channel can be a filtered shunt flow channelwithin the oxygenator, wherein the flow rate through the filtered shuntflow channel is optionally regulatable. In an embodiment, the oxygenatorcan be fluidly connected to a sweep gas reservoir or source via a sweepgas inlet and a sweep gas outlet, wherein the oxygenator comprises sweepgas microtubules in a fiber bundle, and the non-gas-exchange shuntchannel comprises a means of flowing sweep gas selectively to a fractionof the sweep gas microtubules in the oxygenator fiber bundle, whereinnon-gas-exchange shunting occurs within the oxygenator. In anembodiment, the oxygenator is fluidly connected to a sweep gas reservoirvia a sweep gas inlet and a sweep gas outlet, and the means of flowingsweep gas selectively to a fraction of the sweep gas microtubules in theoxygenator fiber bundle comprises a variable flow flap or occlusiondevice, wherein the variable flow flap or occlusion device prevents gasflow through a portion of the fiber bundle near the sweep gas inlet,near the sweep gas outlet, or both, or anywhere along the flow path ofthe fluid from the fluid source. In an embodiment, the oxygenatorcomprises two or more compartments, wherein the flow of sweep gas ineach compartment is independently adjustable. In the embodiment wherethe system comprises more than one oxygenator, each oxygenator can befluidly connected to a sweep gas reservoir via a sweep gas inlet and asweep gas outlet, and each oxygenator can receive fluid from the fluidsource, and the flow of sweep gas to each oxygenator is independentlyadjustable. In an embodiment where the oxygenator comprises two or morecompartments, blood flow to each compartment is independently adjustableso that blood flow may be withheld from some compartments to use only asmuch oxygenating capacity as necessary to achieve the target level ofdissolved oxygen and no more. In an embodiment where multipleoxygenators are used, blood flow to each oxygenator is independentlyadjustable so that blood flow may be withheld from some oxygenators touse only as much oxygenating capacity as necessary to achieve the targetlevel of dissolved oxygen and no more. In an embodiment, the partialpressure of nitrogen at the outlet is reduced or minimized compared withstandard oxygenation strategies incorporating air.

The system and method can be used with any CPB system or circuit,including the system described in WO2015/047927, for example, which ishereby incorporated by reference in its entirety.

EXAMPLES

The following examples are non-limiting. Reference is now made to thedrawings, wherein like reference numerals are used to refer to likeelements throughout the disclosure.

FIG. 1 shows a schematic of an exemplary embodiment of a system usingvenous bypass with a filter to reduce GME. Fluid (which can be gas,liquid, dissolved gas, or a combination comprising one or more of theforegoing) from fluid source 10 passes into optional inflow flowcontroller 20 which controls the flow rate, amount, and othercharacteristics of fluid from fluid source 10 into flow diverter 30.Optional inflow flow controller 20 can be a pump in a CPB circuit. Thebypass and outflow flow controllers, elements 60 and 70, are alsooptional. Optional controller 90 can control inflow flow controller 20,bypass flow controller 60 and/or outflow flow controller 70. Flowdiverter 30 can be any of a number of suitable embodiments, such as atee for diverting a fluid stream into two or more paths, a valve, orother suitable device. Fluid from flow diverter 30 passes intooxygenator 40 and bypass line 100. The percentage of fluid from fluidsource 10 that passes into oxygenator 40 and bypass line 100 can vary,depending on a number of factors, including the amount of a desiredsubstance such as oxygen, or other substance in outlet 80, the desiredfluid volume at outlet 80, or other factors. Oxygenator 40 can be any ofa number of apparatus or systems useful for adding oxygen to a fluid andremoving carbon dioxide. Bypass line 100 includes filter 50. Filter 50can be a so-called “arterial filter”, typically used in CPB to reducethe number and size of GME. Filter 50 can be a screen filter where afilter medium having a desired pore size, as described elsewhere herein,is used to remove particles larger than the pore size of the filtermedium. Filter 50 can be a depth filter, where a filter has a thicknesswhere larger particles are trapped in the surface layers, while smallerparticles are trapped by succeeding layers. The desired pore size orfilter thickness can be varied, to remove or reduce the number ofparticles having a selected size. As an example, a screen filter can beused where the filter medium has a pore size of 50 micrometers, 40micrometers, 25 micrometers, 15 micrometers, or other size that removesGME, but does not filter white blood cells or other desired bloodconstituents, or does not restrict the flow so that the needed ordesired flow rate cannot be achieved. In an embodiment, the filteraccommodates adequate flow rates. The volume, flow rate, or otherparameters of fluid from filter 50 can be controlled by bypass flowcontroller 60. The volume, flow rate, or other parameters of fluid fromoxygenator 40 can be controlled by outflow flow controller 70. Fluidfrom bypass line 100 and oxygenator 40 are combined at outlet 80.

Parameters of the fluid, such as concentration of oxygen, nitrogen,carbon dioxide, anesthesia, medication, or other substance can bemeasured and adjusted at any point, as described herein.

FIG. 2 illustrates an exemplary oxygenator that can be used. In FIG. 2 ,the oxygenator is shown with a housing, a blood inlet and blood outlet,a sweep gas inlet and outlet, and a sweep gas inlet manifold and sweepgas outlet manifold (containing vent openings). The oxygenator is shownhaving a fiber bundle. Water connectors for heat exchange are alsoshown. The oxygenator can use any suitable membrane, such aspolypropylene. Gas vents can be used to control the pressure of theoxygenator.

FIG. 3 shows a heart-lung machine circuit used for the data providedhere.

In FIG. 3 , a CPB bypass circuit with Emboli Detection andClassification (EDAC) and venous air entrainment sites (500 mL/minute)is shown.

FIG. 4 shows experimental data showing that addition of a filter (TerumoAF125x) to the shunt limb (“shunt limb device” in FIG. 3 , for example)effectively limits the shunt fraction to a safe level, and that thislevel is stable over a wide range of CPB flow rates.

FIG. 5 provides experimental data showing that a filtered shunt in theheart-lung machine reduces dissolved O₂ in arterial blood to a safe,mildly hyperoxic, level like that targeted by perfusionists during CPB.The sweep gases were free of nitrogen, so the demonstrated levels ofdissolved O₂ and CO₂ represent the only dissolved gases in the blood.FIG. 5 provides data for three conditions, measurement of the pCO₂ andpO₂ in venous blood from the patient simulator (Condition 1);measurement of the pCO₂ and pO₂ in arterial blood from the heart-lungmachine with the filtered shunt in place (Condition 2); and measurementof the pCO₂ and pO₂ in arterial blood from the heart-lung machine withno shunt (Condition 3). In FIG. 5 , the Y-axes are partial pressures ofdissolved CO₂ or O₂ in mmHg. In FIG. 5 , the X-axes are the conditionsdescribed above.

FIG. 6 provides experimental data showing reduction of GME before (uppergraph titled “Pre Arterial Line Filter”) and after the arterial linefilter (lower graph titled “Post Arterial Line Filter”) when using afiltered shunt compared to control (no shunt). The reduction of GMEafter the arterial line filter is measured downstream of theoxygenator/filtered shunt in question and on the way to the patient. InFIG. 6 , control=no shunt; filtered=filtered shunt; y-axes are emboliper minute; and x-axes are emboli diameter in micrometers.

FIG. 7 provides experimental data showing GME at three locations in theCPB bypass circuit: post pump, post oxygenator, and at the end of theshunt limb (referred to as “Post Shunt Limb” in FIG. 3 ). In FIG. 7 ,control=non-filtered shunt; filtered=filtered shunt; y-axes representemboli per minute; and x-axes represent emboli diameter.

FIG. 8 shows a mathematical model of the sum of the partial pressures asa function of the shunt fraction.

The addition of a filter to the shunt limb reduces shunting of GMEthrough the shunt limb, which is useful to the GME reduction strategyprovided.

Embodiments

The methods and systems are further illustrated by the followingembodiments, which are non-limiting.

Embodiment 1: a system for reducing gaseous microemboli, the systemcomprising a fluid source; a flow diverter fluidly connected to thefluid source, wherein the flow diverter is configured to remove aportion of the fluid from the fluid source; an inflow flow controllerfluidly connected to the fluid source, wherein the inflow flowcontroller is configured to control the flow rate of fluid from thefluid source to the flow diverter; a bypass line fluidly connected tothe flow diverter; a bypass flow controller fluidly connected to thebypass line, wherein the bypass flow controller is configured to controlthe flow rate of fluid from the bypass line; a filter in fluidcommunication with the bypass line, wherein the filter removes gaseousmicroemboli having a diameter greater than a stated pore size,preferably 15 to 50 micrometers; an oxygenator fluidly connected to thefluid source, wherein the oxygenator is configured to oxygenate thefluid from the fluid source; an outflow flow controller fluidlyconnected to the oxygenator, wherein the outflow flow controller isconfigured to control the flow rate of fluid from the oxygenator; anoutlet fluidly connected to the oxygenator and the bypass line; acontroller configured to control the inflow flow controller, the bypassflow controller, the outflow flow controller, or a combinationcomprising at least one or more of the foregoing.

Embodiment 2: The system of Embodiment 1, wherein the oxygenator isconfigured to have a subatmospheric pressure.

Embodiment 3: The system of any of Embodiment 1 to 2, further comprisinga vacuum regulator fluidly connected to the oxygenator, and configuredto provide the subatmospheric pressure.

Embodiment 4: The system of any of Embodiments 1 to 3, wherein theoxygenator is configured to have atmospheric pressure.

Embodiment 5: The system of any of Embodiment 1 to 4, further comprisinga sensor configured to measure one or more of flow rate, fluidcomposition, blood oxygen saturation, oxygen tension, carbon tensionfraction, nitrogen tension, hematocrit, or a combination comprising oneor more of the foregoing, wherein the sensor is fluidly connected to thefluid source, the bypass line, the outlet, or a combination comprisingone or more of the foregoing.

Embodiment 6: The system of any of Embodiment 1 to 5, wherein thecontroller comprises a processor and software instructions implementedby the processor.

Embodiment 7: The system of any of Embodiment 1 to 6, wherein theoxygenator is a membrane oxygenator, a diffusion membrane oxygenator, ora hollow fiber microporous membrane oxygenator.

Embodiment 8: The system of Embodiment 7, wherein the oxygenator is amicroporous membrane oxygenator with a sealed housing.

Embodiment 9: The system of any of Embodiment 1 to 8, wherein the fluidis blood, a blood substitute, artificial blood, a blood product, such asplasma or albumin, platelets or plasma concentrates, crystalloids suchas saline, lactated ringer's solution, normosol, plasmalyte, hetastarch,or a combination comprising at least one of the foregoing.

Embodiment 10: The system of any of Embodiment 1 to 9, wherein the fluidsource is a blender configured to combine one or more fluids.

Embodiment 11: The system of any of Embodiment 1 to 10, wherein a bloodflows within the system.

Embodiment 12: The system of any of Embodiment 1 to 11, wherein theconcentration of oxygen at the outlet is 75 to 800 mmHg, preferably 100to 700 mmHg, preferably 100 to 650 mmHg, preferably 150 to 250 mmHg.

Embodiment 13: The system of any of Embodiment 1 to 12, wherein thepartial pressure of nitrogen at the outlet is reduced or minimizedcompared with standard oxygenation strategies incorporating air.

Embodiment 14: A method for reducing gaseous microemboli, the methodcomprising providing an oxygenator configured to oxygenate a fluid, theoxygenator having a venous inlet, an arterial outlet; a venous bypassline fluidly connected to the venous inlet and the arterial outlet,wherein the venous bypass line comprises a filter configured to removegaseous microemboli having a diameter greater than a stated pore size,preferably 15-50 micrometers, and wherein the venous bypass line isconfigured to remove a portion of the fluid from the venous inlet;introducing a fluid to the oxygenator; oxygenating the fluid passingthrough the oxygenator; combining the fluid from the venous bypass lineand the arterial outlet, forming a combined fluid; wherein theconcentration of oxygen in the combined fluid is 100 to 700 mmHg,preferably 150 to 250 mmHg.

Embodiment 15: The method of Embodiment 14, comprising shunting aportion of the flow through a non-gas-exchange shunt channel is afiltered shunt flow channel within the oxygenator.

Embodiment 16: The method of any of Embodiment 14 to 15, wherein theflow rate through the filtered shunt flow channel is optionallyregulatable.

Embodiment 17: The method of any of Embodiment 14 to 16, furthercomprising limiting the fluid flow passing through the oxygenator.

Embodiment 18: The system of any of Embodiment 1 to 13, furthercomprising a non-gas-exchange shunt channel through the oxygenator.

Embodiment 19: The system of any of Embodiment 1 to 13 or 18, whereinthe non-gas-exchange shunt channel is a filtered shunt flow channelwithin the oxygenator, wherein the flow rate through the filtered shuntflow channel is optionally regulatable.

Embodiment 20: The system of any of Embodiment 1 to 13 or 18 to 19,wherein the oxygenator is fluidly connected to a sweep gas reservoir orsource via a sweep gas inlet and a sweep gas outlet, and wherein theoxygenator comprises sweep gas microtubules in a fiber bundle, and thenon-gas-exchange shunt channel comprises a means of flowing sweep gasselectively to a fraction of the sweep gas microtubules in theoxygenator fiber bundle, wherein non-gas-exchange shunting occurs withinthe oxygenator.

Embodiment 21: The system of any of Embodiment 1 to 13 or 18 to 20,wherein the oxygenator is fluidly connected to a sweep gas reservoir viaa sweep gas inlet and a sweep gas outlet, and the means of flowing sweepgas selectively to a fraction of the sweep gas microtubules in theoxygenator fiber bundle comprises a variable flow flap or occlusiondevice, wherein the variable flow flap or occlusion device prevents gasflow through a portion of the fiber bundle near the sweep gas inlet,near the sweep gas outlet, or both, or anywhere along the flow path ofthe fluid from the fluid source.

Embodiment 22: The system of any of Embodiment 1 to 13 or 18 to 21,wherein the oxygenator is fluidly connected to a sweep gas reservoir viaa sweep gas inlet and a sweep gas outlet, and the means of flowing sweepgas selectively to a fraction of the sweep gas microtubules in theoxygenator fiber bundle comprises a fluid or other suitable substancesuch as water, saline, crystalloid, colloid, blood product, oil, gel,polymer, foam, or wax instilled permanently or reversibly into the sweepgas inlet manifold or the sealed or unsealed sweep gas outlet manifold,or both, in order to prevent flow through a fraction of the sweep gasmicrotubules of the fiber bundle.

Embodiment 22: The system of any of Embodiment 1 to 13 or 18 to 21,wherein the oxygenator housing contains extra ports in dependent ornon-dependent portions of the sweep gas inlet manifold or the sweep gasoutlet manifold, or both, to allow instillation and removal ofsubstances to regulate sweep gas flow in the fiber bundle.

Embodiment 23: The system of any of Embodiment 1 to 13 or 18 to 22,wherein the oxygenator housing contains positive pressure relief valvesin the sweep gas inlet manifold or the sweep gas outlet manifold, orboth, to relieve positive pressures that may result from limitation ofsweep gas flow to a fraction of the fiber bundle.

Embodiment 24: The system of any of Embodiment 1 to 13 or 18 to 23,wherein the oxygenator comprises two or more compartments, wherein theflow of sweep gas in each compartment is independently adjustable.

Embodiment 25: The system of any of Embodiment 1 to 13 or 18 to 24,wherein the oxygenator comprises two or more compartments, wherein theflow of blood in each compartment is independently adjustable.

Embodiment 26: The system of any of Embodiment 1 to 13 or 18 to 25,wherein the system comprises more than one oxygenator, wherein eachoxygenator is fluidly connected to a sweep gas reservoir via a sweep gasinlet and a sweep gas outlet, wherein each oxygenator receives fluidfrom the fluid source, and wherein the flow of sweep gas to eachoxygenator is independently adjustable.

Embodiment 27: The system any of Embodiment 1 to 13 or 18 to 26, whereinthe system comprises more than one oxygenator, wherein each oxygenatoris fluidly connected to a blood reservoir or source via a blood inletand a blood outlet, wherein each oxygenator receives fluid from thefluid source, and wherein the flow of blood to each oxygenator isindependently adjustable.

Embodiment 28: The system of any of Embodiment 1 to 13 or 18 to 27,wherein the partial pressure of nitrogen at the outlet is reduced orminimized compared with standard oxygenation strategies incorporatingair.

Also disclosed is system for reducing gaseous microemboli, the systemcomprising a fluid source; a flow diverter fluidly connected to thefluid source, wherein the flow diverter is configured to remove aportion of the fluid from the fluid source; an inflow flow controllerfluidly connected to the fluid source, wherein the inflow flowcontroller is configured to control the flow rate of fluid from thefluid source to the flow diverter; a bypass line fluidly connected tothe flow diverter; a bypass flow controller fluidly connected to thebypass line, wherein the bypass flow controller is configured to controlthe flow rate of fluid from the bypass line; a filter in fluidcommunication with the bypass line, wherein the filter removes gaseousmicroemboli having a diameter greater than a stated pore size,preferably 15 to 50 micrometers; an oxygenator fluidly connected to thefluid source, wherein the oxygenator is configured to oxygenate thefluid from the fluid source; an outflow flow controller fluidlyconnected to the oxygenator, wherein the outflow flow controller isconfigured to control the flow rate of fluid from the oxygenator; anoutlet fluidly connected to the oxygenator and the bypass line; acontroller configured to control the inflow flow controller, the bypassflow controller, the outflow flow controller, or a combinationcomprising at least one or more of the foregoing.

Also disclosed is a method for reducing gaseous microemboli, the methodcomprising providing an oxygenator configured to oxygenate a fluid, theoxygenator having a venous inlet, an arterial outlet; a venous bypassline fluidly connected to the venous inlet and the arterial outlet,wherein the venous bypass line comprises a filter configured to removegaseous microemboli having a diameter greater than a stated pore size,preferably 15 to 50 micrometers, and wherein the venous bypass line isconfigured to remove a portion of the fluid from the venous inlet;introducing a fluid to the oxygenator; oxygenating the fluid passingthrough the oxygenator; combining the fluid from the venous bypass lineand the arterial outlet, forming a combined fluid; wherein theconcentration of oxygen in the combined fluid is 100 to 700 mmHg,preferably 150 to 250 mmHg.

In any of the foregoing embodiments, the oxygenator is configured tohave a subatmospheric pressure; and/or further comprising a vacuumregulator fluidly connected to the oxygenator, and configured to providethe subatmospheric pressure; and/or the oxygenator is configured to haveatmospheric pressure; and/or further comprising a sensor configured tomeasure one or more of flow rate, fluid composition, blood oxygensaturation, oxygen tension, carbon tension fraction, nitrogen tension,hematocrit, or a combination comprising one or more of the foregoing,wherein the sensor is fluidly connected to the fluid source, the bypassline, the outlet, or a combination comprising one or more of theforegoing; and/or the controller comprises a processor and softwareinstructions implemented by the processor; and/or the oxygenator is amembrane oxygenator, a diffusion membrane oxygenator, or a hollow fibermicroporous membrane oxygenator; and/or the oxygenator is a microporousmembrane oxygenator with a sealed housing; and/or the fluid is blood, ablood substitute, artificial blood, a blood product, such as plasma oralbumin, platelets or plasma concentrates, crystalloids such as saline,lactated ringer's solution, normosol, plasmalyte, hetastarch, or acombination comprising at least one of the foregoing; and/or the fluidsource is a blender configured to combine one or more fluids; and/or ablood flows within the system; and/or the concentration of oxygen at theoutlet is 75 to 800 mmHg, preferably 100 to 700 mmHg, preferably 100 to650 mmHg, preferably 150 to 250 mmHg; and/or further comprising anon-gas-exchange shunt channel through the oxygenator; and/or thenon-gas-exchange shunt channel is a filtered shunt flow channel withinthe oxygenator, wherein the flow rate through the filtered shunt flowchannel is optionally regulatable; and/or the oxygenator is fluidlyconnected to a sweep gas reservoir or source via a sweep gas inlet and asweep gas outlet, and wherein the oxygenator comprises sweep gasmicrotubules in a fiber bundle, and the non-gas-exchange shunt channelcomprises a means of flowing sweep gas selectively to a fraction of thesweep gas microtubules in the oxygenator fiber bundle, whereinnon-gas-exchange shunting occurs within the oxygenator; and/or theoxygenator is fluidly connected to a sweep gas reservoir or source via asweep gas inlet and a sweep gas outlet, and the means of flowing sweepgas selectively to a fraction of the sweep gas microtubules in theoxygenator fiber bundle comprises a variable flow flap or occlusiondevice, wherein the variable flow flap or occlusion device prevents gasflow through a portion of the fiber bundle near the sweep gas inlet,near the sweep gas outlet, or both, or anywhere along the flow path ofthe fluid from the fluid source; and/or the oxygenator is fluidlyconnected to a sweep gas reservoir or source via a sweep gas inlet and asweep gas outlet, and the means of flowing sweep gas selectively to afraction of the sweep gas microtubules in the oxygenator fiber bundlecomprises a fluid or other suitable substance such as water, saline,crystalloid, colloid, blood product, oil, gel, polymer, foam, or waxinstilled permanently or reversibly into the sweep gas inlet manifold orthe sealed or unsealed sweep gas outlet manifold, or both, in order toprevent flow through a fraction of the sweep gas microtubules of thefiber bundle; and/or the oxygenator housing contains extra ports independent or non-dependent portions of the sweep gas inlet manifold orthe sweep gas outlet manifold, or both, to allow instillation andremoval of substances to regulate sweep gas flow in the fiber bundle;and/or the oxygenator housing contains positive pressure relief valvesin the sweep gas inlet manifold or the sweep gas outlet manifold, orboth, to relieve positive pressures that may result from limitation ofsweep gas flow to a fraction of the fiber bundle; and/or the oxygenatorcomprises two or more compartments, wherein the flow of sweep gas ineach compartment is independently adjustable; and/or the oxygenatorcomprises two or more compartments, wherein the flow of blood in eachcompartment is independently adjustable; and/or the system comprisesmore than one oxygenator, wherein each oxygenator is fluidly connectedto a sweep gas reservoir via a sweep gas inlet and a sweep gas outlet,wherein each oxygenator receives fluid from the fluid source, andwherein the flow of sweep gas to each oxygenator is independentlyadjustable; and/or the system comprises more than one oxygenator,wherein each oxygenator is fluidly connected to a blood reservoir orsource via a blood inlet and a blood outlet, wherein each oxygenatorreceives fluid from the fluid source, and wherein the flow of blood toeach oxygenator is independently adjustable; and/or wherein the partialpressure of nitrogen at the outlet is reduced or minimized compared withstandard oxygenation strategies incorporating air; and/or furthercomprising shunting a portion of the flow through a non-gas-exchangeshunt channel which is a filtered shunt flow channel within theoxygenator; and/or the flow rate through the filtered shunt flow channelis optionally regulatable; and/or limiting the fluid flow passingthrough the oxygenator.

All references, including publications, patent applications, and patentscited herein are hereby incorporated by reference to the same extent asif each reference were individually and specifically indicated to beincorporated by reference and were set forth in its entirety herein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) is to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. The terms “comprising,” “having,” “including,” and “containing”are to be construed as open-ended terms (i.e., meaning “including, butnot limited to,”) unless otherwise noted. Recitation of ranges of valuesherein are merely intended to serve as a shorthand method of referringindividually to each separate value falling within the range, unlessotherwise indicated herein, and each separate value is incorporated intothe specification as if it were individually recited herein. All methodsdescribed herein can be performed in any suitable order unless otherwiseindicated herein or otherwise clearly contradicted by context. The useof any and all examples, or exemplary language (e.g., “such as”)provided herein, is intended merely to better illuminate the inventionand does not pose a limitation on the scope of the invention unlessotherwise claimed. No language in the specification should be construedas indicating any non-claimed element as essential to the practice ofthe invention.

Exemplary embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention.Variations of those embodiments may become apparent to those of ordinaryskill in the art upon reading the foregoing description. The inventorsexpect skilled artisans to employ such variations as appropriate, andthe inventors intend for the invention to be practiced otherwise than asspecifically described herein. Accordingly, this invention includes allmodifications and equivalents of the subject matter recited in theclaims appended hereto as permitted by applicable law. Moreover, anycombination of the above-described elements in all possible variationsthereof is encompassed by the invention unless otherwise indicatedherein or otherwise clearly contradicted by context.

What is claimed is:
 1. A system for reducing gaseous microemboli, thesystem comprising a fluid source; a bypass line; an oxygenatorconfigured to oxygenate fluid from the fluid source; a flow diverterfluidly connected to the fluid source, wherein the flow diverter isconfigured to remove a portion of the fluid from the fluid source andthe fluid from the flow diverter passes into the oxygenator and into thebypass line; a non-gas-exchange shunt channel through the oxygenator; afilter in fluid communication with the bypass line, wherein the filteris configured to remove gaseous microemboli having a diameter greaterthan a pore size of the filter; and an outlet fluidly connected to theoxygenator and the bypass line.
 2. The system of claim 1, wherein theoxygenator is configured to have a subatmospheric pressure.
 3. Thesystem of claim 1, further comprising a vacuum regulator fluidlyconnected to the oxygenator, and configured to provide thesubatmospheric pressure.
 4. The system of claim 1, wherein theoxygenator is configured to have atmospheric pressure.
 5. The system ofclaim 1, wherein the oxygenator is a membrane oxygenator.
 6. The systemof claim 1, wherein the oxygenator is a diffusion membrane oxygenator.7. The system of claim 1, wherein the oxygenator is a hollow fibermicroporous membrane oxygenator.
 8. The system of claim 1, wherein theoxygenator is a microporous membrane oxygenator with a sealed housing.9. The system of claim 1, wherein the non-gas-exchange shunt channel isa filtered shunt flow channel within the oxygenator.
 10. The system ofclaim 9, wherein a flow rate through the filtered shunt flow channel isregulatable.
 11. The system of claim 1, wherein the oxygenator isfluidly connected to a sweep gas reservoir or source via a sweep gasinlet and a sweep gas outlet, and wherein the oxygenator comprises sweepgas microtubules in a fiber bundle.
 12. The system of claim 1, whereinthe oxygenator is fluidly connected to a sweep gas reservoir or sourcevia a sweep gas inlet and a sweep gas outlet.
 13. The system of claim 1,wherein the oxygenator comprises an oxygenator housing, wherein theoxygenator housing contains a port in a portion of the sweep gas inletmanifold or the sweep gas outlet manifold, or both, to allowinstillation and removal of substances to regulate sweep gas flow in thefiber bundle.
 14. The system of claim 1, wherein the oxygenator housingcontains a positive pressure relief valve in the sweep gas inletmanifold or the sweep gas outlet manifold, or both, to relieve apositive pressure.
 15. The system of claim 1, wherein the oxygenatorcomprises two or more compartments, and wherein a flow of sweep gas ineach compartment is independently adjustable.
 16. The system of claim 1,wherein the oxygenator comprises two or more compartments, wherein aflow of fluid in each compartment is independently adjustable.
 17. Amethod for reducing gaseous microemboli, the method comprisingoxygenating a fluid in an oxygenator, the oxygenator comprising a venousinlet, an arterial outlet, and a venous bypass line fluidly connected tothe venous inlet and the arterial outlet, the venous bypass linecomprising a filter configured to remove gaseous microemboli having adiameter greater than a stated pore size of the filter, the venousbypass line being configured to remove a portion of fluid from thevenous inlet; and shunting fluid through a non-gas-exchange shuntchannel which is a filtered shunt flow channel within the oxygenator.18. The method of claim 17, further comprising combining fluid from thevenous bypass line and the arterial outlet to form a combined fluid. 19.The method of claim 17, wherein a flow rate through the filtered shuntflow channel is regulatable.
 20. The method of claim 17, furthercomprising limiting the fluid flow passing through the oxygenator.